Fuze for use in firedamp-endangered and coal-dust-endangered operations

ABSTRACT

A fuze for use in firedamp and coal-dust endangered operations suitable for use in the longhole blasting technique which includes a hollow tube, an explosive core of desensitized explosive surrounding the hollow tube, a wound strip of plastic encasing the explosive core, a multiple-layer spun casing of fibers enclosing the wound plastic strip and an envelope of inert substances surrounding the multiple-layer spun casing. The envelope is, preferably, a mixture of a polymer and insert substances covered, respectively, by cellulose-base fibers, a wound strip of plastic, a multiple-layer spun envelope of fibers, and finally a waterproof outer shell of synthetic resin.

[451 any 1, 1973 Elite States n 1 Heligeni et al.

3,344,005 9/1967 Bronstein et al. ..............'........149/93 3,590,739 6/1971 Persson...............................102/27 R FOREIGN PATENTS OR APPLICATIONS 1,916,685 12/1970 Germany............................102/27R both of 521 Troisdorf, Germany [7}] Assignee: Dynamit Nobel AG, West Germany Primary Examiner-Verlin R. Pendegrass Attorney-Craig, Antonelli & Hill [22] Filed: Oct. 28, 19711 [21] Appl. No.: 193,460

' ABSTRACT A fuze for use in firedamp and coal-dust endangered [30] Foreign Apphcauon Prwnty Data operations suitable for use in the longhole blasting cludes a hollow tube, an explosive core of desensitized explosive surrounding the hollow tube, a wound strip of plastic encasing the explosive Nov. 20, 1970 Germany.....................P 20 57 042.7 echnique which in us. Cl.

102/27 R ...F42b 5/04 core, a multiple-layer spun casing of fibers enclosing ...102/27 R, 70 R; the wound plastic strip and an envelope of inert substances surrounding the multiple-layer s The envelope is, preferably, a mixture 0 L C in n In.

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f a polymer and insert substances covered, respectively, by cellulose-base fibers, a wound strip of plastic, a multiple- References Cited UNITED STATES PATENTS layer spun envelope of fibers, and finally a waterproof outer shell of synthetic resin.

102/27 R 102/27 R Grandy et al. ......................102/27 R 17 Claims, 1 Drawing Figure m t e n h o D 592 456 999 111 W64 iNVENTORfi WERNER HELFGEN WILHELM ROHDE BY 016 nmvmwv ATTORNEYS FUZE FOR USE IN FIREDAMP-ENDANGERED AND COAL-DUST-ENDANGERED OPERATIONS This invention relates to a fuze for use in firedampendangered and coal-dust-endangered operations, which can initiate with certainty the conventional safety mining explosives.

Special interest has existed for a long time, for example in coal mining, in providing a fuze which can be used without any danger in all blasting operations carried out in coal mining. The demand for such a fuze is particularly acute in mines with a steep disposition of bituminous coal seams, where coal mining with the use of conventional mining and extracting machines is impossible. ln this connection, plans exist for mining the bituminous coal by the so-called longhole blasting procedure in order to eliminate the more expensive, complicated mining by means of air hammers (rock drills, jackhammers). When blasting via very long shot holes, electric primers cannot be utilized. In this case, only a fuze (priming cord) which does not represent any danger for mine gas mixtures (firedamp) at the given length of the shot holes, e.g. 20 m., is suitable. Thus, the fuze must be firedamp-proof. In addition, the fuze must be able to initiate with certainty all conventional and mining-approved explosives of classes II and Ill.

Since a fuze satisfying these requirements and suitable for approval by the mining authorities has not been in existence heretofore, the present invention is based on the problem of developing a fuze which meets all demands from the viewpoint of blasting technology and simultaneously possesses a maximum degree of firedamp dafety.

The fuze of the present invention is characterized by a core cord having a strongly reduced explosive weight per meter of fuze, of a powdery desensitized explosive, with a hollow tube centrally disposed within the explosive core and a casing of inert substances having a flash-reducing (flame-cooling) and flame-baffling ef-- feet. The combination of the individual features of the core cord and the casing, as well as their mutual adaptation result in a surprising increase in the firedamp safety of the fuze which has not existed heretofore. Thus, it is possible to utilize the instant fuze in firedamp-endangered and coal-dust-endangered operations without the occurrence of a firedamp explosion.

In the construction of the fuze, the individually provided measures result, by their cooperation, in the special, firedampproof characteristics. The starting point is the quantity of the explosive to be utilized. Since the capability of an explosive to ignite firedamp does not solely depend on the brisance and explosion temperatures, but is influenced to the same extent by the amount of the explosive employed, the core cord of this invention is equipped with an explosive core having an explosive weight which is strongly reduced as compared to the customary fuze, ranging preferably between 2 to 5 g. per meter. With such an amount, a compact, solid explosive core will assume outer diameters ofonly 2.6 to 3.0 mm.

In order to ensure, with such a small amount of ex- I plosive, a safe complete detonation, a second measure is provided, namely the use of a powdery explosive in an extremely finely divided form, wherein at least 60 percent of the explosive passes through a mesh screen of 0.074 mm. In spite of the small weight and the small diameter of the explosive core, a flawless complete detonation is then achieved due to the pulverized form of the explosive. A suitable explosive is, for example, penthrite.

The third measure essential to the present invention is the addition of a desensitized substance to the powdery explosive. For this purpose, all materials can be employed which genuinely reduce the brisance of the explosive, such as, cryolite, all halogenides, sulfates, bicarbonates, carbonates, and phosphates of the alkali metals and alkaline earth metals, the corresponding ammonium salts, and all oxides of the alkaline earth metals. However, care is to be taken in the selection of the desensitizirtg substance so that, with a minimum quantity of additive, a satisfactory desensitization is effected without endangering the complete detonation or detonation propagation of the explosive core. Cryolite proved especially suitable since it exhibits excellent flame-cooling properties.

The fourth essential measure is the central arrangement of an endless hollow tube in the explosive core. This hollow tube provides, as a result of its characteristic, a hollow-charge effect, i.e. the tube effects, up to a certain extent, a directional shot which focuses a large portion of the energy liberated during the reaction of the explosive in the axial direction of the fuze and thus strongly reduces the normal uniform lateral effect. This hollow tube, which must be adapted to the diameter of the explosive core with respect to its diameter, exhibits an optimum efficiency in cooperation with the explosive employed when occupying about one-third of the total (or outside) diameter of the explosive core. The hollow tube consists, for example, of any desired, deformable and stretchable synthetic resin and is uniformly round and disposed as centrally as possible within the explosive core. This tube should furthermore exhibit a uniformly round hollow channel which is not constricted or interrupted by pressure, bending or other mechanical influences.

The thus-formed core cord is surrounded, in a fifth measure essential to the present invention, by a casing of inert substances having a flame-cooling and flamebaffling effect. The important feature of this casing is the density of the envelope of gas vapors and firing vapors formed by the vaporization of the inert substances. A dense envelope is capable of absorbing residual, laterally effective energies, hot explosion gases and glowing particles of the core cord to shield and screen off the same against any existing explosive gas mixtures, e.g., firedamp. As the inert substances suitable for producing such a dense envelope, all the materials set forth above for the desensitization of the explosive can be employed. However, especially advantageous is a mixture of inert substances and powdery synthetic resins, both thermosetting and thermoplastic synthetic resins being suitable, admixed in an extremely fine distribution to the other inert substances in a percentage of S- percent based on the weight of the other inert substances. Synthetic resins on the basis of polyacrolynitrile with styrene and butadiene or ABS- polymers are particularly preferable. However, other heat-resistant plastics can be successfully utilized in this connection, for example, polytetrafluoroethylene, or copolymers of polyacrylonitrile.

As an external seal and for protection against moisture, the encased core cord is advantageously surrounded by an outer shell, e.g., of extruded plastic, such as soft PVC.

In the drawing, an embodiment of the fuzeof this invention is illustrated which will be explained in greater detail hereinbelow.

The foundation of the so-called core cord is formed by the plastic hollow tube 1 disposed centrally with respect to the longitudinal axis. Tube 1 is surrounded and guided by several threads 2 which, in turn, are surrounded by explosive core 3 of, for example, a uniform mixture of 4 g. of extremely fine penthrite with percent (0.4 g.) of cryolite, per running meter of fuze. The strip 4 of plastic, e.g., hard PVC, encases, wound in overlapping windings, the explosive core 3. The multiple-layer spun casing 5 of natural and/or synthetic fibers forms the outer cover of the core cord.

The envelope of the core cord is constituted by the jacket composition 7 of inert substances, e.g., 8 g. per running meter of fuze of a mixture of 50 percent ABS (acrylonitrile-butadiene-styrene) polymer, percent cryolite and 30 percent sodium chloride. This mixture is likewise guided in the axial direction by several threads 6, for example of cellulose-base fibers. The cover of the fuze comprises: strip 8 of a plastic film, e.g., hard PVC, wound in overlapping windings; the multiple-layer spun envelope 9 of threads of synthetic and/or natural fibers; and the waterproof outer shell 10, e.g., of soft PVC.

A thus-constructed fuze exhibits a detonation velocity of 6000 i 600 m./sec., a tensile strength of 100 :t 20 kp./cm. and an outer diameter of about 5.8 mm.

The fuze of this invention, which is' distinguished by an especially high degree of firedamp safety, was tested in the chamber of an explosive testing range in various arrangements having 9 9.5 percent firedamp concentrations.

Prior to each testing blast, a firedamp ignition was triggered by means of conventional Al primers in the chamber. Subsequently the fuze of the invention was test fired with a standard test primer (detonator) No. 8, tied laterally to one end of the fuze. As demonstrated below, contrary to Al primer, the fuzes ofthe invention did not ignite the firedamp.

a. Test in a box mortar with a wall spacing of d 20 cm. and angle of impingement of a 100 at a single position:

Length of Fuze Result 2 m. Three times no ignition of firedamp b. Testing of the fuze horizontally suspended freely in the center of the chamber:

Total length Result of fuze Length of Number of Strands cut strands used fuze bundle fuze strands (open) on both sides 6 m. 2 m. 3 Three times no ignition of firedamp c. Testing of the fuze freely suspended vertically in the center of the chamber:

In further experiments with the fuze as constructed according to the invention, every one of the permitted safety explosives of classes [I and III was initiated, without the safety with respect to firedamp being impaired.

Conventionally in the manufacture of a fuze, the covering method is advantageously employed, wherein the explosive is introduced from a feeding funnel into a thin strip of paper, plastic or another suitable material which is continuously helically wound in overlapping windings at the lower end of the funnel. The explosivefilled strip is then provided with a cover of various layers of textile threads or the like twisted from fibers, which are helically wound or spun therearound. Thereafter, the core cord is encased with the inert mixture of substances in the same manner, and the thus-obtained fuze additionally provided with a coat of varnish, a thermoplastic synthetic resin or the like. In the present invention, however, since the powdery explosive utilized does not exhibit fluidity it is introduced into the core cord from the feeding funnel by means of transporting threads with a rough surface traveling through the filling funnel under tension and vibration. The use of such transporting threads exhibits the additional advantage that these threads enhance the central positioning of the hollow tube within the core fuze, since the threads simultaneously constitute a support for the hollow tube.

We claim:

1. A fuze for use in firedampand coal-dust-endangered operations comprising an explosive core having a hollow center and including a powdery desensitized explosive of a strongly reduced explosive weight per meter of fuze, a hollow tube disposed within the hollow center of said explosive core, and a casing of inert substances surrounding said explosive core and having a flame-cooling and flame-baffling effect.

2. A fuze according to claim 1 wherein said explosive is present in an amount of between about 2 and about 5 g./m.

3. A fuze according to claim 1 wherein said explosive is pulverized penthrite, at least 60 percent of which passes through a screen mesh of about 0.074 mm.

4. A fuze according to claim 1 wherein said explosive is desensitized by a substance selected from the group consisting of cryolite, halogenides, sulfates, bicarbonates, and carbonates of the alkali and alkaline earth metals, the corresponding ammonium salts, and all oxides of the alkaline earth metals.

5. A fuze according to claim 4 wherein 10 percent by weight of cryolite based on the weight of explosive is added to said explosive.

6. A fuze according to claim I wherein said hollow tube is constructed of a flexible, dimensionally stable synthetic resin.

7. A fuze according to claim '6 wherein the diameter of said .hollow tube is about one-third of the outside diameter of said explosive core.

8. A fuze according to claim 1 wherein said casing is comprised of a mixture of at least one powdery synthetic resin and at least one substance selected from the group consisting of cryolite, halogenides, sulfates, bicarbonates, and carbonates of the alkali and alkaline earth metals, the corresponding ammonium salts, and all oxides of the alkaline earth metals.

9. A fuze according to claim 8 wherein between about 5 percent and about 70 percent of synthetic resin particles are admixed with said at least one inert substance.

10. A fuze according to claim 8 wherein said at least one synthetic resin is based on polyacrylonitrile with styrene and butadiene.

11. A fuze according to claim 1 further comprising an outer shell of extruded synthetic resin disposed around said casing.

112. A fuze according to claim 1 further comprising a strip of wound plastic disposed between said explosive core and said casing of inert substances.

13. A fuze according to claim 12 further comprising a multiple-layer spun envelope of synthetic or natural threads positioned between said strip of wound plastic and said casing of inert substances.

14. A fuze according to claim 13 further comprising a second strip of wound plastic covering said casing of inert substances.

15. A fuze according to claim 14 further comprising a second multiple-layer spun envelope of synthetic or natural threads encasing said second strip of wound plastic.

16. A fuze according to claim 15 further comprising an outer shell of extruded synthetic resin disposed around said second multiple-layer spun envelope.

17. A fuze according to claim 16 further comprising first and second thread groups, respectively, wound in a manner so as to guide the distribution of said powdery desensitized explosive and said inert substances. 

2. A fuze according to claim 1 wherein said explosive is present in an amount of between about 2 and about 5 g./m.
 3. A fuze according to claim 1 wherein said explosive is pulverized penthrite, at least 60 percent of which passes through a screen mesh of about 0.074 mm.
 4. A fuze according to claim 1 wherein said explosive is desensitized by a substance selected from the group consisting of cryolite, halogenides, sulfates, bicarbonates, and carbonates of the alkali and alkaline earth metals, the corresponding ammonium salts, and all oxides of the alkaline earth metals.
 5. A fuze according to claim 4 wherein 10 percent by weight of cryolite based on the weight of explosive is added to said explosive.
 6. A fuze according to claim 1 wherein said hollow tube is constructed of a flexible, dimensionally stable synthetic resin.
 7. A fuze according to claim 6 wherein the diameter of said hollow tube is about one-third of the outside diameter of said explosive core.
 8. A fuze according to claim 1 wherein said casing is comprised of a mixture of at least one powdery synthetic resin and at least one substance selected from the group consisting of cryolite, halogenides, sulfates, bicarbonates, and carbonates of the alkali and alkaline earth metals, the corresponding ammonium salts, and all oxides of the alkaline earth metals.
 9. A fuze according to claim 8 wherein between about 5 percent and about 70 percent of synthetic resin particles are admixed with said at least one inert substance.
 10. A fuze according to claim 8 wherein said at least one synthetic resin is based on polyacrylonitrile with styrene and butadiene.
 11. A fuze according to claim 1 further comprising an outer shell of extruded synthetic resin disposed around said casing.
 12. A fuze according to claim 1 further comprising a strip of wound plastic disposed between said explosive core and said casing of inert substances.
 13. A fuze according to claim 12 further comprising a multiple-layer spun envelope of synthetic or natural threads positioned between said strip of wound plastic and said casing of inert substances.
 14. A fuze according to claim 13 further comprising a second strip of wound plastic covering said casing of inert substances.
 15. A fuze according to claim 14 further comprising a second multiple-layer spun envelope of synthetic or natural threads encasing said second strip of wound plastic.
 16. A fuze according to claim 15 further comprising an outer shell of extruded synthetic resin disposed around said second multiple-layer spun envelope.
 17. A fuze according to claim 16 further comprising first and second thread groups, respeCtively, wound in a manner so as to guide the distribution of said powdery desensitized explosive and said inert substances. 